The G2 vehicle his company is developing is largely built from sustainable materials including an interior of recycled plastic bottles and tyres made from natural rubber.
It won't be on the road until the cash needed to finish design work and begin production - amounting to $150 million - can be raised.
"With all the other start-ups that have failed over the past couple of years this is a daunting task," Mr Saul told the Herald. "We continue to do design work but at a much slower pace - but one day we will be absolutely thrilled to see lots of G2s driving around New Zealand."
Mr Saul expected an eventual strong take-up of green cars from Kiwis because of their reputation for environmental stewardship and New Zealand's unique geography.
"I believe smaller cities and less congestion would reduce range anxiety and make electric vehicles more acceptable to the population."
There had already been interest in the G2 from Hawaii and nations in the Caribbean and the Bahamas which have limited distance driving.
"Also, there is a large potential for renewable energy."
Green cars also appealed because they were cheaper to run than standard models.
"When you factor in the significant reduction in maintenance cost, you can make a real argument for saving money over the long term.
"You also have a hedge against rising fuel costs with plug-ins as electricity rates are much more stable than oil and there is very little correlation between their costs."
Electric motors were up to 97 per cent efficient compared with about 30 per cent for a modern petrol engine, he said.
Improvements in technology, such as cylinder deactivation, direct injection and start-stop systems, had lifted petrol-engine efficiency but it was still well below 40 per cent.
"As the price of oil rises as we start to run out of it, which we're already seeing, plug-ins will become more and more attractive.
"New Zealand can benefit directly for reasons of national security. As an island nation, if the oil supply ever gets cut off, for example due to geopolitical instability, the use of plug-in vehicles could make a major impact on securing transportation for critical services."
But Mr Saul conceded there were downsides to green cars.
Among the biggest was range anxiety - worrying about running out of power while driving - but this wasn't a concern for plug-in hybrids. "Another is the cost, the size and weight of the battery packs and lastly the lack of charging station infrastructure."
The good news, he said, was that batteries were becoming cheaper and better.
The G2
The "G2" that American company Generation Cars is developing has a lightweight green composite body made from soy bean resin, not petrochemicals, and basalt fibre. Its "green interior" is made using recycled plastic bottles. The tyres are made from natural rubber, not oil. Superior aerodynamics and light weight combine to boost the range per kWh of battery energy. The company plans to build green factories powered by renewable energy.
